Isolated medial meniscus allograft transplant intraoperatively restores anteroposterior knee stability as effectively as isolated anterior cruciate ligament reconstruction

Purpose: To compare the capacity of isolated medial or lateral meniscus allograft transplantation (MAT) and isolated anterior cruciate ligament (ACL) reconstruction (ACLR) to reduce pre-operative knee laxity in vivo. Isolated MAT was hypothesized to restore knee stability comparably to isolated ACLR. Methods: All surgical procedures performed with intraoperative navigation were retrospectively analyzed. Patients with post-meniscectomy syndrome and intact ACL undergoing medial or lateral MAT (MAT-M and MAT-L groups) were matched 1:1 by age and sex to patients with intact menisci undergoing ACLR (ACLR-M and ACLR-L groups, respectively). Intraoperative anteroposterior (AP), internal/external rotation, varus/valgus and pivot-shift (PS) laxity were quantified using the navigation system before and after surgery. Repeated-measures ANOVA was used to compare laxity between groups across pre- and post-operative states. Statistical significance was set at p < 0.05. Results: From a total of 232 patients, 36 were selected: 8 in the MAT-M group, 8 in the ACLR-M group, 10 in the MAT-L group and 10 in the ACLR-L group. MAT-M reduced pre-operative AP laxity with no statistically significant difference compared to ACLR, across all measured parameters, including AP translation at 30° and 90° of flexion, internal/external rotation and varus-valgus. Conversely, ACLR was a significantly more effective stabilizer compared to MAT-L, demonstrating a greater reduction in AP laxity at 30° (43.2% vs. 37.2%, p = 0.045) and 90° of flexion (62.6% vs. 36.3%, p = 0.007), and PS area (62.5% vs. 32.5%, p = 0.002). Conclusions: In patients with chronic post-meniscectomy syndrome, isolated MAT-M restored AP knee stability comparably to isolated ACLR, suggesting that the medial meniscus acts as a primary stabilizer in this population. In contrast, isolated MAT-L was significantly less effective than ACLR in controlling AP and PS laxity, despite significantly reducing it. These findings highlight the critical, compartment-specific biomechanical role of the menisci. Level of Evidence: Level III.